The invention relates to a method and apparatus for continuous renal replacement therapy. More particularly, this invention relates to a method and apparatus for compensating for extracorporeal heat loss from a patient undergoing continuous renal replacement therapy.
When a patient experiences renal failure, one of several extracorporeal blood treatment processes may be performed in order to replace the function of the failed kidneys. The processes include, without limitation, dialysis, ultrafiltration, hemofiltration, and hemodiafiltration, all of which, and similar processes, will be referred to herein collectively as xe2x80x9cdialysis.xe2x80x9d Further xe2x80x9cdialyzerxe2x80x9d as used herein will be understood to mean a dialyzer, hemofilter or similar device. In the event of chronic, or permanent, kidney failure, also known as end stage renal disease, or ESRD, dialysis is usually performed at relatively high blood flow rates for around three or four hours, typically thrice per week. This type of periodic treatment challenges the patient""s body, but is well tolerated by most ESRD patients as it offers them the opportunity for a relatively normal life.
Acute kidney failure, from which a patient may, in time, recover is often accompanied by other injuries or underlying disease which render the patient""s body unable to withstand the rigors of periodic dialysis. These acute patients are usually treated at relatively lower blood flow rates and treated continuously. Also, very young patients are often unable to withstand the rigors of periodic dialysis and are often treated at low blood flow rate and/or continuously. This form of dialysis will be referred to herein as continuous renal replacement therapy or CRRT.
A method and apparatus for CRRT including equipment and disposable elements, is described in U.S. Pat. Nos. 5,394,732, 5,441,363 and 5,676,245 which are incorporated herein in their entirety by reference. Further, an apparatus for performing CRRT is sold by affiliates of the assignee of the present application under the tradename PRISMA(trademark).
In dialysis some heat is generally lost to the environment from the blood circulating in the extracorporeal circuit, which, in time, results in loss of heat from the patient""s body. In periodic treatment, the body""s metabolic processes usually compensate for this heat loss and the patient""s corporeal temperature is not significantly depressed. The continuous nature of CRRT increases the heat loss potential of the blood circulating in the extracorporeal circuit and the patient may, under certain circumstances, experience a depression of corporeal temperature.
It is, therefore, desirable, in some CRRT treatments, to compensate for heat loss from the patient""s blood circulating extracorporeally. Fluid heaters have been used to heat either dialysate or infusate fluid. Typical blood flow rate in CRRT is approximately 120 ml/min while dialysate flow rate is typically 1 to 2 l/hr (16-33 ml/min). In order to transfer heat energy from the dialysate to the blood, it is necessary for the average temperature of the dialysate to be significantly higher than the average temperature of the blood. In the heat transfer zone between the dialysate and blood, which is typically a dialyzer or hemofilter, it is, under these circumstances, possible for the local blood temperature to be significantly higher than the average blood temperature. Average corporeal temperature in a healthy human patient is about 37xc2x0 C. At local blood temperatures above 42xc2x0 C., the blood may experience denaturing and flocculation of proteins and hemolysis.
Heating of the infusate fluid presents similar problems with regard to blood damage. Further, heat transfer from the infusate to the blood would be by direct mixing rather than across a dialyzer membrane further increasing the risk of blood damage. In addition, infusate flow is generally pumped, which means that it flows under negative pressure. Heating the infusate under negative pressure conditions can cause de-gassing of the infusate introducing air and other gas bubbles into the fluid flow. The resulting air may cause operational difficulties including the need to extract air from the CRRT system and excessive air embolism protection operation.
An affiliate of the assignee of the present invention produces a blood component separation centrifuge which includes an electric blood warmer under the trade name SPECTRATHERM(trademark). A former affiliate of the assignee produces oxygenation systems for use in cardiopulmonary bypass surgery which incorporates fluid-to-fluid blood heat exchangers for heating and cooling blood under the tradenames, without limitation, CML(trademark), VPCML(trademark), OPTIMA(trademark) and K+ARDIA(trademark). Baxter Healthcare has suggested that a blood warmer may be used for CRRT in conjunction with its BMlla(trademark) blood pump.
It is against this background that the significant advances of the present invention were made.
It is an object of the present invention to provide an integrated CRRT method and apparatus which incorporates steps and means for compensating for heat loss from blood in an extracorporeal circuit. It is a further object of the invention to limit the local temperature experienced by the blood into levels which are not expected to damage the blood. It is a further object of the invention to minimize the generation of gasses which can cause operational problems in a CRRT method and apparatus. It is a still further object of the present invention to maintain adequate patient pressure and air embolism protection. It is a still further object of the present invention that the heat loss compensation method and apparatus be selectively usable. It is yet another object of the present invention to minimize the extracorporeal blood volume of a CRRT system when heat loss compensation is not required. Further objects of the present invention will be apparent from the detailed description of the preferred embodiment.
A significant aspect of the present invention for achieving at least one of the objects is a CRRT apparatus incorporating a blood warmer designed to engage and hold a disposable blood tube segment to transfer heat at a closely controlled temperature to blood flowing in the disposable blood tube segment. Another significant aspect of the present invention for achieving at least one of the objects is a blood tube segment for engagement with the blood warmer which is located in flow communication with and downstream of a dialyzer and upstream of one or combination of a venous pressure monitor, an air bubble detector and a venous line clamp. A further significant aspect of the present invention for achieving at least one of the objects is a dialysis disposable tubing set with which a disposable blood tube segment in the form of a blood line extension for engagement with the blood warmer may be selectively connected when heat loss compensation is required and left disconnected when heat loss compensation is not required.
Further significant aspects of the present invention will be apparent from the drawings, and from the detailed description of the preferred embodiment.